Conventionally, to produce useful chemicals heavy hydrocarbon fractions, such as vacuum gas oil (VGO), are catalytically cracked with a catalyst in a fluidized cracking process. During this process, the catalyst typically circulates between a catalytic reactor and regenerator. In the catalytic reactor, hydrocarbons come in contact with hot catalysts that have been supplied from the regenerator and the hydrocarbons are cracked to produce gasoline, LPG, and dry gas. Coke is also produced during this process and is deposited on the catalyst. The cracked products are typically then separated from the coked catalyst in cyclone separators. Volatiles are stripped with steam and the coked catalyst is then sent to the regenerator. Regenerated catalyst particles are then recirculated to the reactor.
The product slate from conventional FCC process primarily consists of gasoline, in addition to light olefins, dry gas and LPG. Light olefins, particularly propylene, are increasingly gaining importance to refiners, as these products can increase refinery profit margins due to their high value. Propylene, which is used in the manufacture of various synthetic materials, particularly materials that are used in food packaging industry and thermoplastics, is in high demand. Additional demand for propylene exists in the area of alkylate production, which is increasingly being used as an additive for high-octane gasoline, due to environmental concerns raised by the use of olefins-containing FCC gasoline and aromatics-containing catalytically reformed gasoline. Propylene and butylene are the raw materials for the alkylate additive.
Small pore zeolites from the pentasil zeolite family, such as ZSM-5, have been previously used as catalysts in FCC operations. Additionally, pentasil zeolites have been used as additives in traditional FCC catalysts for the purpose of increasing light olefin yields. Prior art methods, however, suffer from the production of low yields of useful and desired light olefins. Thus, due to the various uses for tight olefins, such as propylene, there exists a need for increased production and/or improved efficiency in the production of propylene.